Not familiar with either sumac or chicken brush, but bet I've dealt with their equivilant. On nasty brush with large stems, sometimes I'll back up a deck length, with the mower set high, and drop the deck, and mow my way out. Very hour intensive, customers hate it. If at all possible, take a half bite,or a half of the mowers capacity. I keep the tractor more or less centered in the tall stuff. The mower has a clockwise rotation, the second pass hits the leftover stems from the other direction, and pretty much finishes them off. Have used that pattern on any ground that you can go foward on. Doesn't work so well on places that are too steep to drag the mower behind you